1. Field of the Invention
The present invention relates to an electrostatic chuck, and more particularly to an electrostatic chuck to prevent generating an arc.
2. Discussion of the Related Art
Most apparatus of fabricating semiconductor devices use an electrostatic chuck to fix a wafer. However, there is a problem that an arc is generated at the electrostatic chuck when a radio frequency (RF) bias is applied to the electrostatic chuck.
FIG. 1 is a schematic cross-sectional view of a conventional electrostatic chuck.
In FIG. 1, an inner electrode 25 is formed on a metal plate 10 and a dielectic layer 20 is formed on the inner electrode 25, whereby the inner electrode 25 is interposed between the dielectric layer 20 and the metal plate 10. For example, If a polyimide layer If formed on a copper electrode, the polyimide layer and the copper electrode respectively become the dielectric layer 20 and the inner electrode 25. A wafer 30 is loaded on the dielectric layer 20. A wall 50 of a process chamber is grounded. After the wafer 30 is loaded on the dielectric layer 20 and process gases are injected into the process chamber, a first RF power is applied through an additional plasma electrode (not shown). As a result, a plasma 40 is generated in the process chamber. The plasma 40 functions as a conductor connecting the wall 50 of the process chamber arid the wafer 30. Here, if a negative voltage is applied to the Inner electrode 25, a clamping force that the wafer 30 and the metal plate 10 attract each other with the dielectric layer 20 interposed therebetween is generated. Accordingly, the wafer 30 is chucked onto the dielectric layer 20. A second RF power is applied to the metal plate 10 from the same power source of the first RF power or from an additional power source so that positive ions of the plasma can collide against the wafer 30 with a higher momentum due to a self-bias. Especially, this application of the second RF power is desirable to a plasma etching process such as a reactive ion etching (RIE). Moreover, the clamping force that the wafer 30 is chucked onto the dielectric layer 20 increases due to the self-bias.
Since the wafer 30 is heated due to a collision of ions during a plasma etching process, an injection hole 15 of a cooling gas is formed through the metal plate 10 and the dielectric layer 20 to cool the wafer 30. Generally, a helium (He) gas is supplied through the injection hole 15 and spread out on an entire surface of the dielectric layer 20 through a groove (not shown) formed on the dielectric layer 20. Since the wafer 30 is loaded on the dielectric layer 20, the supplied cooling gas does not leak out of the dielectric layer 20. Moreover, a lift pin hole 17 also formed through the metal plate 10 and the dielectric layer 20 and an ejection of the wafer 30 is promoted by an up-and-down movement of a lift pin 19 through the lift pin hole 17.
In the conventional electrostatic chuck, an arc is generated at one end “A” of the lift pin hole 17 and one end “B” of the injection hole 15 when the RF power is applied to the metal plate 10. Especially, the arc much more occurs for the lift pin hole 17 because the lift pin hole 17 has a longer diameter than the injection hole 15. Even though the wafer 30 is chucked onto the dielectric layer 20, the cooling gas such as He gas supplied through the injection hole 15 flows to the lift pin hole 17, thereby generating the arc at the end of the lift pin hole 17. If the cooling gas such as He gas near the end of the lift pin hole 17 is heated by a local increase of a temperature of the wafer 30, the wafer 30 and the electrostatic chuck are damaged by a plasma discharge generated at the lift pin hole 17.